In GSM networks, the trace facility enables customer administration and network management to trace the activities of various entities when specific events occur. This facility enables the tracing of information available to the network concerning the call path used by the associated entity. The information that could be in a trace record may comprise e.g. the identity of the originating and terminating equipment of the concerned mobile or fixed subscriber, the identity of the incoming and outgoing circuits of the nodes involved, supplementary services invoked, interface messages, etc. The trace facility is a useful maintenance aid and development tool which can be used during system testing and proving. It may be used by subscriber administration and network management for subscriber observation, e.g. following a customer complaint or on suspicion of equipment malfunction by the operator or at a request of the police (i.e. lawful interception). As the amount of information that can be collected for a single call is very large, network elements can limit the number of simultaneous traces by either rejecting a trace request or by only producing a sub-set of the information required.
An activation of a trace is an action taken by an operation system function (OSF) or an operation and maintenance center (OMC) through MMI (Man Machine Interface) commands to allow a trace to be produced for a particular IMSI (International Mobile Subscriber Identity) or IMEI (International Mobile station Equipment Identity) when an invocation event occurs. An invocation of a trace is an event relating to a particular IMSI or IMEI, which occurs in the network and which causes data to be collected in a trace record in circumstances where the trace has been activated for that IMSI or IMEI. The trace action and record layout is defined by the trace type parameters of the corresponding trace request.
A trace can be invoked in a Base Station Subsystem (BSS) of the GSM network when an invoking event specified in a trace type parameter of a trace request occurs and a BSS record type is set to a value indicating that the tracing function is activated. Furthermore, a trace can be invoked by sending a corresponding message from a Mobile Switching Center (MSC) to the BSS. When the BSS receives this message, it starts tracing the necessary fields as specified in the BSS record associated with the specified BSS record type.
If the subscriber is roaming within its home network, the trace request is forwarded to the Visitor Location Register (VLR) where the subscriber is registered via a message indicating an active trace mode. If the subscriber is roaming in a foreign mobile network, the home network subscriber trace request is stored in the Home Location Register (HLR), but the trace is not active in the VLRs of the home network. In order to trace the IMSIs of roaming subscribers in the own network, a list of those IMSIs plus the associated subscriber trace parameters must be stored in the VLR. The network operator may then activate a trace for any foreign roaming IMSI from an OSF by invoking a corresponding management function, i.e. transmitting a trace request to the respective VLR serving the subscriber. If the location of the subscriber is not known, it is necessary to activate the trace in all VLRs where the subscriber may be located. The trace request is stored in the VLR. If the subscriber subsequently roams into the VLR area, the subscriber trace will be activated in the visited network.
In order to achieve access independence and to maintain a smooth interoperation with wireless terminals across the Internet, Internet Protocol multimedia subsystems (IMSs) have been developed with an attempt to conform to Internet standards set out be the IETF (Internet Engineering Task Force). Therefore, interfaces specified conform as far as possible to IETF standards for those cases where an IETF protocol, e.g. the Session Initiation Protocol (SIP), has been selected.
The IMN enables operators of mobile networks to offer their subscribers multimedia services based on and built upon Internet applications, services, and protocols. There are two possible scenarios to provide services, i.e. via the service platform in the home network or via an external service platform (e.g. a third party or visited network). Call State Control Functions (CSCFs) are provided which can act as Proxy CSCFs (P-CSCFs), Serving CSCFs (S-CSCFs) or Interrogating CSCFs (I-CSCFs). The P-CSCF is the first contact point for a user equipment within the IMN. The S-CSCF actually handles the session states in the network. The I-CSCF is mainly the contact point within an operator's network for all connections destined to a subscriber of that network operator. A more detailed description of the IMN can be gathered from the 3GPP specification TS 23.228.
However, the Third Generation Partnership Project (3GPP) has not specified any trace solution for the Internet Protocol (IP) Multimedia Subsystem (IMS) of Universal Mobile Telecommunications System (UMTS) networks. Therefore, no trace is possible in multi-vendor networks.
Furthermore, the H.248 standard does not disclose how to activate the tracing in the MGW, which is not possible using prior art techniques if the user and control planes are separated.